If the coolant temperature is well above the thermostat rating then the coolant temperature should drop when the car is sitting at idle in gear with both fans on.

The coolant temperature should easily remain just above the thermostat rating when driving, especially when driving faster then about 35-40mph.

In your case, you see 200* when idling but you can make the temperature climb and then it won't come back down. Well, it should at least drop back to 200*.

2000CFM, is that one fan or both fans added together? Seems low for both fans.

The fan operation - How are they wired? When do they come on?

Direction was asked, have you checked that the fans suck into the engine compartment?

Seal were asked, do you have the factory type seals around the rad and support?

Air dam was asked, do you have it?

 

What exhaust do yo have bolted to the manifolds and what is your timing set at?

 

So i have had no progress with the car. I will try to answer all the questions that I remember.

the air dam is on the car.

the gaskets are not but i just ordered some

these are the fans i have on the car http://www.haydenauto.com/upload/Hay...ctric_Fans.pdf

I have 1 of the 16" fans and 1 14" fan as that is what would fit


I put a temp gun on the top hose going in the radiator
(220) and then the bottom hose coming out of radiator (215) so it seems like the radiator is not doing its job. but like I said the under hood temps are super high.

the timing is set to 10degrees with the advance caped off at idle

i also ordered a high flow summit water pump to see what that does. But at this point I feel like I'm just throwing parts at the car with no results.

if that doesn't work I'm taking the motor out and tearing it down to see if i can see something in the motor that is just wrong and creating to much heat.

I'm pulling my hair out at this point and not sure what to do.

thank you for everyone that has taken the time to help.

geo

 

What is the timing at idle with the vacuum advance connected?

 

I would try 16* advance at idle.
I also think 5* drop in radiator is squat.
Radiator is not cooling.

 

Here's something else for your consideration. I am new to the Corvette world, purchasing a 1999 convertible with 54,000 miles a year ago. Both my wife & I love it!

Normal highway driving at 70 mph, my coolant temp stays at 190 degrees. We live close to the Black Hills of South Dakota. Each time we've cruised the winding, steep grades of the Hills, my temp gauge will go as high as 230-240 degrees, with outside ambient temperatures in the 60's or 70's. As soon as we return to normal highway driving, the temp gauge returns to 190. After the first experience, I had the cooling system flushed with no difference.

Recently, I drove on a hot 100 degree afternoon and the temp gauge rose to 220 at normal highway driving. Still concerned, I took it to our Chevrolet Dealer for a check over, last week. The report said: "Scanned- no codes. Tested cooling fans- low and high speed working properly, low at 219 degrees, high at 228 degrees. Coolant Full. System operating properly at this time." They also told me that the radiator looked good.

Question for you experts: Are these temps normal? Do I trust the Dealer's Tech guy and quit worrying about it?

Thanks, John

 

You are grasping at straws now. Don't do that, big waste of time.

Try the high flow water pump, can only help, more flow higher pressure, almost always beneficial. If you don't need the heat, then you can block off the heater connection at the pump and manifold. You will then recirculate less hot coolant.

Make sure your distributor is working properly.
Reconnect your vac advance and test with a light to make sure total timing is correct thru all rpms including the mechanical weights. Err on the high side if anything. With a new alum rad, you should see a minimum of 20° temp difference at the rad.


JF Ranch
There is virtually no way a dealer tech can see if the rad is plugged or not, especially on flat rate time.
Good chance that flushing the system even plugged it more, especially alum ones.
Some rads just are too far gone.

You can get a brand new rad for 60 bucks.
How much have you already paid the dealer.
Bought many of them, work just fine.

 

This is an interesting subject, but i am not one of the experts here,

Me, i dont like my cars over 200, but my cars are old school, no computers, no worries about emissions or government regulations.

Gm had to meet government regulations, some of that required running the cars hotter, and of course gm says its fine, they are designed that way, but look at how some c7 guys who try to drive their cars a bit harder have cooling system woes.

Oddly tons of forum posts and magazine articles have been devoted to getting these later dating back to c4s cars to run cooler, you will see those cats saying they believe their cars run better a little cooler,

So my jaded person opinion car manufactures have to do what they can within the confines of regulations doesnt mean its always best,
What does gm say your car should run at?
i would likely trust that the dealers tests they can do came back clean, but my OCD would drive me nuts to see 240 even when pushing on it a little,

 

before tearing things apart try and figure out where your flow restriction is that is causing the lower hose to collapse and try and get an oil temp reading, maybe you can shot the temp of the oil pan once up to temp.

Neal

 

geoology

For what it is worth I have a 1978 at my shop right now that is in for problems in the cooling system. To make this quick...the engine runs fine at about 200 degrees around town but when the A/C is turned on it will go up to 205 or 210 degrees when driving and then really climb if I am stuck in traffic. I put my racing temp gauge in it to make sure the factory gauge was reading correctly and YEP...it can get to 240 degrees if I am sittign still with the A/C on. ALL seals are installed and air dam in place.

I actually removed the fan clutch and used one of those fan clutch eliminator and that did not help at all. So I know it is not air movement. I has one of the Robert Shaw thermostats in it when I installed the rebuilt engine a few years ago.

I have one of the Stewart stage one water pumps that is going to go on it and that is because I was hearing a bearing noise in the water pump...so maybe that will help ...BUT...I HONESTLY feel I need to pull out the copper /brass four row radiator and have my radiator guy pull off the tanks and rod it out. And it was NEW few years ago...but I do not trust the stuff being made today when it comes form across the pond.

SO I FEEL your pain....and know how it can get to you.

I seriously doubt it is in your engine.

JF Ranch

Honestly I feel you do not have a problem because if these high temps are occurring when you are driving up a grade for an extended period of time...you are aware that the engine is under a lot more stress than if it were on flat ground. I would not label that type of drive and 'highway driving' it would be more like HARSH driving..and not that you are abusing your car.. but more that the conditions your car is being put under are harsh.
Kinda like brake pad companies can make brake pads for an 18 wheeler that will work about 98% of the time correctly...but going down a mountain...they can heat up and fail...due to the harsh conditions.

I am not saying that if these temperature bother you that you could not find someone to modify the cooling system IF these trips to the mountains is going to be a common occurrence.

I know that this is true because if I can ride my bike when I am at my sisters house in south Florida for 15 miles and not even get overworked due to it is FLAT...but if I rode my bike in Charlotte where there are hills...I can tell you my lungs are about to pop out of my chest.

I DO agree that the tech can not look at your radiator and say that it is fine. And I DO KNOW that on the pre-1997 Corvettes..they are notorious for having pine needles and bird feathers ,etc blocking the area of the radiator in front of the primary cooling fan. But what this generally does is causes the cooling fan to not pull the temp down quickly when they are on. Reading that your temps go down I doubt that that is a problem...but maybe worth a look-see.

DUB

 

I am a cattle rancher, definitely not a mechanic. Could you explain to me how flushing the system could plug it up? The car is a 1999, so the original radiator is 18 years old but it only has 60,000 miles on it now. Are the years harder on it than the miles? Thanks!

 

I should talk personally with the Tech about what they say the car should run at. This is a large dealership and I've not succeeded in getting past the service desk so far. But he tested both fans and said they are working properly. Low at 219 degrees and High at 228. Wouldn't this mean that temps in the 220-230 range be acceptable?

 

Stop by your local tool store and buy a IR temp reader. Check various temps throughout the system.

Thermostat housing, radiator inlet, radiator outlet etc...

 

Sorry if I hi-jacked Geo's thread. Thanks to all who responded. I'll let you all return to Geo's problem.

 

Temps are 'normal' for when the fans should turn on. The real question is it 'normal' for temps to run that high on the highway? No, its not. C5's are 'bottom feeders' I'll venture a guess and say you have a ton of crap in front of your radiator and in between the radiator and condenser. Common issue with C5's....Check C5 gen.

Bunch of youtube videos as well.

 

The tubes in almost all alum rads are narrower than brass rads and can just plug up much easier.
When flushing properly some of the scale is dissolved but some is just loosened and flows into the tubes and plugs them.
Like I said earlier, a new rad is 60 bucks plus shipping, certainly worth it if the rest of the system is clean.

You can also try a colder tstat and see if that makes a difference. If not then flashing your chip for lower fan activation temps should help.

 

I AGREE that 'flushing' a coolant system can do more harm than good....especially if it has been neglected. I have seen some coolant systems that must have had the original coolant from the facotry in it And the crap and scale was so bad when I removed the block drains it was ridiculous. Knowing that even when I attempted to get it clean was going to release more crud and it was going to create more problems.

From my experiences...putting in a colder thermostat does little to nothing at all due to all it is doing is causing the thermostat to open sooner...but in the long run...and the car being driven and obviously the thermostat is open...the engine coolant temp will go back to the problem area again.

I do agree with possible flashing the fans on sooner.....but if teh thermostat is open and flowing coolant..and the fans can not do their job and the temps get back to where they were ...then it is in the radiator.

DUB

 

The colder tstat and/or flash will only work if the radiator is in great shape.
Plugged or partially plugged radiators is akin to having far too small a radiator.

I'll say it again, as inexpensive as radiators are today, don't even contemplate it, just replace them.

 

Do you still have the stock catalytic converter on the car?

 

Thanks for all the help.

Again, this C5 is new to me. I bought it a year ago with about 54,000 miles on it. It now has 60,000. I assume the catalytic converter and radiator are both original.

I took it to a large Chevrolet Dealer to check the cooling system. It tested OK and they did not do any work on it. I wanted to talk personally with the Tech but could not get past the service desk. The service guy assured me that this Technician is their top one, very thorough and would not cut corners or miss anything. Both fans tested correctly and the same Dealership flushed the system for me last fall. They are saying that the cooling system is working properly at this time.

Aside from the radiator perhaps getting old and whatever Kacyc3 is suggesting with the converter, here is what I think might be going on.

From earlier posts, I've read that the car needs enough air flow or ground speed to cool properly. The Black Hills driving that I've referred to has steep grades and very winding roads. The engine works fairly hard and average speeds might be 15-20 mph, with only 5 mph on the many hairpin curves.

Additionally, several earlier posts stressed the importance of having the front air dam in place for proper air flow. Our car does not. The middle section of the 3 piece air dam has been missing since I bought the car. The previous owner probably scraped it off on curb stops and it was never replaced.

Do you think the combination of the missing air dam coupled with relatively low speeds in this type of driving is causing the coolant to heat to 230 plus degrees? Again, as soon as we have driven out of the Hills and returned to normal highway driving, it cools right down to 190-200.